Merlin Guest Blog: Ben Bosma

Guest Blog from Engineer Ben Bosma:


Here are the first versions of the new Merlin instrument panel. 90% of the information is presented by the MGL iEFIS. I pasted the iEFIS into this picture. Chip will have an actual one on this panel at Sun N Fun.

The rest is technology we’re developing. First, the engine information is normally channeled through a box from MGL. We are developing our own mainly because we can. The data coming from the ECU has everything we need from the engine. Second, we’re using printed circuit boards with microprocessors to do our switches. All the switches are dual pole for redundancy. We are also using fuses which are difficult to see when they blow. That’s what the LEDs are for. They light when a fuse blows. The fuses are standard automotive products and can be replaced from the front panel. All of that is on the left. On the right is the fuel panel and fuel pump control. There are two fuel pumps. They are plumbed so that you can use either pump or both. If a pump fails, you have a backup. Part of the preflight will be to check each pump. If a pump fails a red LED indicates which one is out. The other pump bypasses the bad pump with a check valve.

Why not circuit breakers? Have you priced them, lately? There’d be about $1000 in breakers in this panel vs about $10 in fuses and $20 in holders.

Above those switches is a left-auto-right switch for tank selection. We are using an automotive fuel tank selector valve that is electric. It has dual spools that allow both the supply and return to be switched.

This allows us to instantly switch tanks and since it’s electric we can automate the tanks switching either by time or quantity always keeping the tanks balanced. Of course, you can manually override the automatic tank switching by simply selecting the desired tank. Fuel management is the third highest cause of accidents. Engine out work with fuel in one tank and dry in the other is not okay.

There are fuel senders in each tank which display the quantity in each tank at all times. Since, we have a microprocessor on each board, we’ll just ask it to do a little bit more for us.

Automatic tank selection is something you don’t see on most GA aircraft. It’s a jet thing. Of course, there will be lights indicating the feeding tank.

The panel is hinged on the bottom so you can easily wire and inspect your wiring. It’s not a big panel. 22-1/2″ wide. It’s got everything you need within easy reach.



The V-Twin is a very advanced engine not just with its induction system which has dual overhead cams and electronic ignition but also, it’s cooling system which is entirely liquid-cooled.
Originally, we were using commercial cooling hoses joined with aluminum tubes, nipples and connections. This looked cobbled together and although perfectly adequate was heavy and too complex. So, we now have custom silicone hoses that are molded to our specification. While we were at it, we also designed and had built a custom radiators and custom coolant cans.
The radiator is in the prop disc so even though the ECU has a coolant sensor and fan control we don’t need it. Temperature is controlled with a mechanical thermostat in the coolant loop just like a car.
We put the coolant can at the highest point in the loop and has a 1.3bar cap and overflow tank.
Our hose vendor gave us a broad choice of colors. We picked blue. What do you think?
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